1. Field of the Invention
The invention relates to a solenoid valve.
2. Description of the Prior Art
A conventional solenoid valve, particularly for a hydraulic assembly, which is used for instance in an anti-lock brake system (ABS) or a traction control system (TC system) or an electronic stability program (ESP system), is shown in FIG. 1. As seen in FIG. 1, the conventional solenoid valve, which is embodied for instance as a two-stage on-off valve that is closed when without current, includes a valve cartridge 1, which includes a pole core 2, a valve insert 4 connected to the pole core 2, an armature 3 guided axially movably inside the valve insert 4 and coupled with a primary closing element 7, and a valve body 8 connected to the valve insert 4, which body, with the primary closing element 7 and a primary valve seat 9, forms a primary valve disposed between at least one first flow opening 12 and a second flow opening 13, and via the axial motion of the armature 3 and of the primary closing element 7, the primary valve seat 9 is opened counter to the force of a restoring spring 5 and closed by the force of the restoring spring 5, and an air gap 6 between the armature 3 and the pole core 2 predetermines a maximum possible stroke of the armature 3. The valve body 8 and the valve insert 4 are each embodied as a sleeve and are connected to one another.
Because of the two-stage embodiment, a secondary valve, which is formed by a secondary closing element 11 that is connected to the armature 3 and by a secondary valve seat 10 that is disposed in the primary closing element 7, has a smaller sealing diameter and flow, so that an opening of the secondary valve counter to a high pressure, which results in a partly active or preloaded pressure buildup, is made possible. The primary valve with the primary valve seat 9, which has a large seat cross section, and the primary closing element 7 make a large flow possible which is as unthrottled as possible and which results in a fully active or self-aspirating pressure buildup. A magnet assembly, not shown, by supplying current to a coil winding, generates a magnetic force which moves the longitudinally movable armature 3 with the secondary closing element 11 counter to the force of a restoring spring 5 against the pole core 2, as a result of which the secondary valve seat 10 is opened. By means of the pressure equilibrium effected upon the opening of the secondary valve seat 10 between the at least one first flow opening 12 and the second flow opening 13, a compression spring 14 reinforced by fluid flow forces moves the primary closing element 7 in the direction of the armature 3 or the secondary closing element 11, as a result of which the primary valve seat 9 suddenly opens and the secondary valve seat 11 closes again. In this conventional solenoid valve, the annoying hydraulic noises that occur upon opening of the primary valve in the preloaded mode, which are also known as fluid-borne sound, can be considered disadvantageous.